Phosphate laser glass has an advantage that its stimulated emission cross section is large, but encounters disadvantages that, in addition to poor mechanical strength and poor chemical durability, thermal shock resistance is poor due to its large co-efficient of thermal expansion. Such disadvantages of phosphate laser glass can be improved to a certain extent by incorporation R".sub.2 O.sub.3 (wherein R" represents Y, La, B or Al) or R'O (wherein R' represents Mg, Ca, Sr, Ba, Zn or Pb; hereafter the same) into the glass composition.
On the other hand, a silicate laser glass generally has excellent mechanical strength and thermal shock resistance, but has a small stimulated emission cross section and a large concentration quenching. As a result, a large amount of Nd.sub.2 O.sub.3 cannot be doped in the glass.
Investigations were made in a laser glass
(1) to increase a thermal shock resistance;
(2) to decrease a concentration quenching and reduce moisture, thereby increasing a stored energy; and
(3) imparting a relatively small stimulated emission cross section, thereby reducing a parasitic oscillation.